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Browse CatalogHigh-Performance Liquid Chromatography, commonly known as HPLC, is the workhorse technique for both purifying and analyzing synthetic peptides. If you have ever looked at a Certificate of Analysis from NXPeptides or any other peptide supplier, the purity value listed there almost certainly came from an HPLC analysis. This guide explains how HPLC works in the context of peptide science, the different methods used, and what the results mean for your research.
At its core, HPLC is a separation technique. It works by passing a liquid sample through a column packed with a solid material (the stationary phase) under high pressure. Different components in the sample interact differently with the stationary phase and therefore travel through the column at different speeds. This separates the mixture into its individual components, which are detected as they exit the column.
For peptides, HPLC serves two purposes: it is used during manufacturing to purify the crude synthesis product (removing incomplete sequences, deletion products, and other impurities), and it is used analytically to measure the purity of the final product.
The most common HPLC method for peptides is reversed-phase chromatography. In RP-HPLC, the stationary phase is hydrophobic (usually C18 or C8 bonded silica), and the mobile phase is a mixture of water and an organic solvent, typically acetonitrile, with a small amount of trifluoroacetic acid (TFA) as an ion-pairing agent.
Here is how it works in practice:
By collecting only the fraction that corresponds to the target peptide peak, the manufacturer obtains a purified product. The width and shape of the peak also provide information about the quality of the synthesis.
Most peptide HPLC separations use gradient elution rather than isocratic (constant composition) conditions. In a gradient run, the mobile phase composition changes over time, typically going from a high water / low organic ratio to a high organic / low water ratio.
A typical analytical gradient might look like this:
The gradient rate and starting conditions are optimized for the specific peptide being analyzed. Longer, shallower gradients provide better resolution between closely related impurities but take more time.
As separated components exit the HPLC column, they pass through a UV detector. Peptides absorb UV light strongly at 214 to 220 nm (due to the peptide bond) and at 280 nm (if they contain tryptophan or tyrosine). The detector records the absorbance over time, producing a chromatogram.
On the chromatogram, each peak represents a different component. The area under a peak is proportional to the amount of that component. Purity is calculated by comparing the area of the target peptide peak to the total area of all peaks:
Purity (%) = (Area of target peak / Total area of all peaks) x 100
So when your COA says 99% purity, it means that 99% of the total UV-absorbing material detected was your target peptide.
There are two distinct scales of HPLC used in peptide production:
Preparative HPLC is used during manufacturing to actually purify the peptide. It uses larger columns, higher flow rates, and processes milligram to gram quantities. The goal is to collect the pure peptide fraction while discarding the impurity fractions.
Analytical HPLC is used for quality control. It uses smaller columns and tiny sample quantities (micrograms). The goal is not to collect anything, but simply to measure the purity and obtain the chromatographic profile. The purity data on your COA comes from analytical HPLC.
NXPeptides offers peptides at several purity grades. Here is what the numbers mean in practical terms:
For most research purposes, 98% purity strikes the right balance between quality and cost. If your application requires the absolute highest purity, let us know and we can discuss options for your custom synthesis project.
Several factors can influence HPLC results, which is why standardized methods are important:
This is why comparing HPLC results between different labs or suppliers can be tricky unless the same method was used. At NXPeptides, we use validated, standardized methods for all our quality control testing, as described on our Quality Assurance page.
While HPLC is excellent for measuring purity, it does not tell you everything. That is why it is used alongside other analytical methods:
Together, these techniques provide a comprehensive quality profile for each peptide batch.
Questions about the HPLC data on your COA? Reach out to us at support@nxpeptides.com or via our Contact page. Our quality team is happy to walk you through the data.
All NXPeptides products are for research purposes only. Not for human consumption.